1. Field of the Invention
This invention relates to reactive polyamide resins and especially organic solvent-free polyamide resins for curing epoxy coating resins. More particularly, this invention relates to polyamide resins made from a C.sub.21 -cycloaliphatic dicarboxylic acid that are soluble up to about 45% by weight when water is added to the resin.
Epoxy resin surface coatings hardened with reactive polyamide resins have achieved continued growth due to their excellent resistance to corrosion and strong chemicals, their good adhesion properties, and their resistance to abrasion, impact, and other physical abuse. The largest use for epoxy surface coatings is coatings for cans and closures. Despite the advantages, epoxy coatings have the disadvantage of needing organic solvents during application. Although water-dispersible epoxy resin coating systems have been developing slowly, there remains in these systems need for an organic solvent to solubilize the polyamide resin prior to dispersion in water. Also, these systems require dispersants and emulsifiers harmful to the properties of the hardened coating.
2. The Prior Art
Efforts to obtain epoxy coating using polyamide resins in aqueous systems are represented by U.S. Pat. No. 2,811,495 to Wittcoff et al. which discloses first solubilizing a polyamide resin and an epoxy resin separately in an organic solvent and then dispersing the solubilized resins into water. U.S. Pat. No. 2,899,397 to Aclony et al. also discloses mixed aqueous emulsions of polyamide resins and epoxy resins solubilized with hydroxylic solvents and then dispersed in water.
This invention provides a method of eliminating the need for an organic solvent by using a particular dibasic acid and a method of solubilizing. The polyamide resin used in the method of this invention is disclosed in British Pat. No. 1,046,208 to Crawford et al. The polyamide resins of Crawford et al. were found to be satisfactory hardening agents for epoxy resins and were diluted with organic solvents.
It is the general object of this invention to provide a process for making water-dilutable reactive polyamide resins.
Another object of this invention is to provide an organic solvent-free method for producing epoxy resin surface coatings.
Other objects, features and advantages of this invention will be apparent from the foregoing detailed description of the invention.